Virtual reality can be viewed as a computer-generated simulated environment in which a user has an apparent physical presence. A virtual reality experience can be generated in 3D and viewed with a head-mounted display (HMD), such as glasses or other wearable display device that has near-eye display panels as lenses to display a virtual reality environment, which replaces the actual environment. Augmented reality, however, provides that a user can still see through the display lenses of the glasses or other wearable display device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as a part of the environment. Augmented reality can include any type of input such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that a user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality, from generation of the virtual objects and images so that they appear realistic in a real environment, to developing the optics small and precise enough for implementation with a wearable display device.
A challenge to the implementation of wearable display devices, such as a head-mounted display (HMD), for virtual and/or augmented reality is that one size does not fit all users. Just as typical users come in all shapes and sizes, so is the interpupillary distance between different users' pupils of their eyes. Additionally, the distance from a user's nose to the pupil of one eye may be different than the distance from the user's nose to the pupil of the other eye. For binocular viewing systems, such as a wearable display device, the right and left display lens systems have a small lateral margin to approximately center a user's eyes on the optical axis of the display lens systems. This small lateral margin of adjustment for varying interpupillary distances is commonly referred to as the eyebox for a display lens system, and the eyebox represents the range within which a user's eye should be positioned for viewing with a wearable display device. Some conventional systems attempt to compensate for the uniqueness of different users with a mechanical adjustment system, which is then a wearable display device that fits only one person. Another compensation technique is to oversize the eyebox for a general, one-size-fits all approach. However, this is largely cost-prohibitive due to the expensive optical systems in wearable display devices. Additionally, the one-size-fits all approach to oversize the eyebox results in a very large and heavy optical system, which is also impractical for consumer head-mounted display systems.